The invention relates to drive units for vehicles. Preferred embodiments of the invention are especially suitable for cases of installation in which a specific axle offset is to be overcome in the course of the power transmission from the engine to the wheels. When the two part transmissions are connected advantageously and when the total transmission ratio is allocated in a suitable way according to the present invention, better transmission efficiencies are achieved in comparison with normal drives.
A practical example can be an automobile design with a transverse engine and front-wheel drive. To ensure an economical engine drive, it is necessary for the transmission to have 5 forward gears and for the power transmission from the engine to the wheels to have as few losses as possible. However, the space available as an extension of the engine crankshaft is often not sufficient to install a five-speed transmission of standard design in the vehicle.
The invention is especially concerned with drive units for motor vehicles of the type in which the axes of rotation of the main shaft of an engine and of an input wheel of an intermediate transmission are arranged in line with one another in relation to one of two parallel geometrical main axes, and in which the axes of rotation of an output shaft, connectable to a differential, of a first pick-off member gear-change transmission of epicyclic design, of a transmission member connected fixedly in terms of rotation to the output shaft and belonging to a first epicyclic transmission and of the output wheel of the intermediate transmission are arranged in line with one another in relation to the other main axis, the input shaft of the gear-change transmission can be driven from the main shaft, and the output wheel can be brought into drive-connection with an outer central wheel transmission member of the epicyclic transmission which has the transmission member connected fixedly in terms of rotation to the output shaft.
In a known drive unit of this type (German Offenlegungsschrift No. 1,650,840, FIG. 1), a Ravigneaux transmission is used for the gear-change transmission. This transmission has two inner central wheels and an outer central wheel, two gear clutches and two gear brakes, is assigned completely to the main axis of the output wheel of the intermediate transmission and provides three forward gears and one reverse gear. The axis of rotation of the differential coincides with a third geometrical main axis lying parallel to the other two main axes. It is also known from this publication to provide, instead of one gear clutch, a second intermediate transmission which, however, ensures only a constant drive connection between a hydrodynamic torque converter, driven by the engine, and one inner central wheel, whilst the other intermediate transmission is driven directly by the main shaft and is connected to the remaining gear clutch of the other inner central wheel. The number of forward gears is, however, not increased as a result of this second intermediate transmission.
In a further known drive unit of this general type (German Auslegeschrift No. 1,625,125), a Ravigneaux transmission or the like, formed from two twin-coupled single-web epicyclic transmissions and having four free transmission members, is used to achieve four forward gears by means of power branching via a second intermediate transmission, one free transmission member being couplable to the output wheel via a drive clutch located at one transmission end and via one intermediate transmission, two other free transmission members being couplable independently of one another to the turbine wheel of a hydrodynamic torque converter via two drive clutches located at the other transmission end and via the other intermediate transmission, and the fourth free transmission member being connected to the output shaft. However, the gear-change transmission, together with the drive clutches and the gear brakes, is assigned completely to the main axis, parallel to the main axis of the main shaft, of the output wheels of the two intermediate transmissions.
It is known from U.S. Pat. No. 3,482,469, in another drive unit of this general type, in order to achieve six to eight forward gears, to connect the output shaft to one transmission member of a single-web epicyclic transmission or of a Ravigneaux transmission, to connect another transmission member of this transmission to a further Ravigneaux or Simpson transmission and to connect two drive shafts extending from a hydro-dynamic torque converter, each by means of an intermediate transmission located at a particular end of the gear-change transmission assigned as a whole to the main axis parallel to the main axis of the main shaft, to the two epicyclic transmissions via an appropriate number of drive clutches, in such a way that these epicyclic transmissions interact in series or individually with the torque converter.
An object of the invention is primarily to achieve a compact design, which is short in the directions of the main axes, in a drive unit of the above-mentioned general type. According to preferred embodiments, such compact design includes a hydrodynamic torque converter which is arranged in the flux of force in series between an engine and a gear-change transmission having at least five forward gears and which preferably operates with a bridging clutch.
The above-mentioned objects are achieved according to preferred embodiments of the invention by providing a drive unit wherein the axes of rotation of the input shaft of a drive clutch and of a transmission member couplable to the input shaft by means of the drive clutch and belonging to an epicyclic transmission which has a transmission member which can be brought into drive-connection with the input wheel, are arranged in line with one another relative to the main axis of the main shaft.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.